Overprint is a way of combining colors when dealing with
subtractive color spaces such as CMYK or DeviceN.
Normally, when one color is painted over another, it replaces
the underlying color. So a black over a cyan becomes yellow. If
Overprint is set, then the top color may be placed over the top of
the base color. So black over cyan becomes a mixture of both black
and cyan inks. This can be useful for printing purposes.
In ABCpdf, overprint is only applied when the Overprint property
is set to true, the output ColorSpace
is CMYK, the IccOutput is "device", the
PDF graphics state indicates that overprint mode should be applied
(see the Adobe PDF
Specification for details) and no transparency has been